How to add a watermark in simple blend4web turntable scene exported as .html by using either Blender or directly coding in .html?
There is a special feature in B4W called Viewport Alignment. Using this feature, the object can be aligned to the active camera, so that the object will remain in the same place of the screen regardless of the position and rotation of the camera. This is especially useful for creating UI elements and watermarks.
Taken from the B4W manual.